Escherichia coli DNA-binding protein H-NS is localized in the nucleoid

Electron microscope localization of the 15.4-kDa DNA-binding protein H-NS was carried out in Escherichia coli cells subjected to cryosubstitution followed by immuno-labelling with the protein A/gold technique. Three types of E. coli cells were used: (1) "normal" cells growing exponentially at 37 degrees C; (2) "cold-shocked" cells two hours after the shift from 37 degrees C to 10 degrees C; and (3) cells in which an expression vector had been induced to overproduce H-NS. The results clearly indicate that in all 3 cases, the vast majority of the molecules reacting with anti-H-NS antibodies are localized within the nucleoid and at the border between the nucleoid and the ribosome-rich cytoplasm, which supports the premise that H-NS is implicated in the condensation of the nucleoid.